1. Field of the Invention
This invention relates generally to pre-filled syringes for administering various fluids into a patient, more particularly, the invention relates to plastic syringes for injecting liquid pharmaceutical/biological agents, such as diagnostic imaging agents, into a patient.
2. Reported Developments
Various syringes for taking body fluid samples or administering fluid medicaments to a patient are known. Such syringes generally include a cylindrical syringe barrel, a hypodermic needle engaged with the syringe barrel, and a plunger within the syringe barrel which, when a force is exerted axially by an operator, create a suction force drawing body fluids into the barrel, or delivers fluid medicament through the hypodermic needle. The purpose of the plunger is to provide an air tight seal between itself and the syringe barrel so that movement of the plunger up and down the barrel will allow liquid, blood or other fluids to be drawn into or forced out of the syringe through the distal end.
Syringes used for such purposes include glass syringes, in which the cylindrical barrel is made of glass and the plunger is a ground glass rod which closely fits within the cylindrical barrel. In order to eliminate leakage and at the same time reduce resistance to an acceptable level, close tolerances are necessary between the barrel and the plunger along with the use of a lubricant. These glass syringes suffer from a number of disadvantages including that: they are expensive since they require close tolerances; they cannot be easily mass produced since the plungers often cannot be interchanged with one another and have to be individually fit with the barrel during the grinding process by the manufacturer; and they are susceptible to breakage.
To obviate these problems syringes were proposed and/or made by using glass and plastic barrels with plastic or elastomeric plungers. In order to prevent leakage around the plunger, the plunger is made with one or more ribs which are slightly larger in diameter in the uncompressed state than the inside of the barrel which upon placement within the barrel are compressed and deformed against the wall of the barrel and thereby form a seal. The quality and strength of the seal depend on the elastomeric properties of the material used to make the plunger and the ratio of the respective diameters of the plunger and the inside of the barrel. To obtain a good leak-proof seal, a relatively large compressive force must be exerted on the elastomeric plunger by the syringe barrel. This quality of seal, however, makes the movement of the plunger within the barrel difficult requiring excessive force on the part of the operator to move the plunger. This drawback is even more pronounced with pre-filled syringes which are maintained, ready to use, in storage. During this shelf-life the plunger tends to seize in the barrel. To remedy the problem the prior art used lubricants to reduce friction and drag between the plunger and the inside of the syringe barrel. One of the commonly used lubricants for this purpose is silicone oil. The use of such lubricants is, however, undesirable, since the lubricants tend to disperse and/or dissolve in parenteral formulations thereby contaminating the formulations. Such potential adulteration is, of course, undesirable and attempts were made to avoid the use of lubricants and still provide a leakage-proof syringe with easily slideable plunger. Such attempts included the use of various plunger configurations including one or more ribs thereon projecting forwardly or rearwardly in the barrel to reduce the frictional drag between the plunger and the barrel. Another approach was, for example in U.S. Pat. No. 5,009,646, to laminate the elastomeric plunger with a film of tetrafluoroethylene, ethylenetetrafluoroethylene and ultrahigh molecular weight polyethylene resin.
While liquid tightness and sliding property have somewhat improved with these attempts as regards to syringes intended for taking body fluid samples or injecting medicaments from stored vials, the problem of inadequate sliding property in pre-filled syringes stored for extended time periods still remain unsolved.
It is a main object of the present invention to provide a pre-filled syringe and a pre-filled cartridge which will overcome the above-described inadequate sliding property while maintaining a tight, leak-proof seal between the plunger and the wall of the syringe barrel.
It is another object of the present invention to provide a self-aspirating syringe and cartridge.
In medical practice, hypodermic injections are sometimes administered subcutaneously, while others must be given intravenously, depending upon the particular medication to be administered. In either case, it is essential that the practitioner know with certainty, prior to injection of the medication whether the hypodermic needle tip is located in a major blood vessel, such as a vein, or in subcutaneous tissue. Use of an aspirating syringe in which a negative pressure can be generated in the syringe affords a means of making such determination. Thus the appearance of blood in the syringe upon generation of the negative pressure would indicate location of the needle tip in a major blood vessel, while the lack of appearance of blood would indicate location of the tip in subcutaneous tissue. Depending upon the type of injection intended, the injection can then either proceed directly or if appropriate, the tip can be withdrawn and relocated.
Aspirating syringes are generally of two types, namely, they are either manually or automatically aspirated. In the manually aspirated type the plunger is retracted for a short distance within the barrel of the syringe. This retraction lowers the pressure within the syringe which leaves fluids at the needle tip which are then observable within the barrel of the syringe. From solid tissues no fluids will be drawn into the barrel. In the manually aspirated syringes the injection necessitates the use of both hands, one to hold the barrel, and the other to exert pressure in a rearward direction on the plunger. Such manually actuatable aspirating syringes have the disadvantage that their proper use depends on very large measure on the degree of skill of the person administering the injections.
Aspiration in syringes of the automatic or self-aspirating type is effected by first inducing a positive pressure in a medicament-containing portion of the syringe. On release of the force inducing the positive pressure, a corresponding negative pressure in the syringe is generated thus giving rise to the aspirating effect. The present invention relates to the self-aspirating type syringes.
Ideally a self-aspirating hypodermic syringe should be: relatively simple in construction so as to minimize the cost of production; should be relatively simple to operate; should be capable of manipulation with one hand; should be adaptable to multiple self-aspirating actions; should be capable of expelling trapped air from the ampoule prior to insertion of the needle into the injection site and prior to initiation of the self-aspirating action without either precluding self-aspirating action at a later time in the operation sequence of the syringe or otherwise rendering it inoperative.
The self-aspirating syringes provided by the present invention mimic, automatically, the slight rearward piston displacement withdrawal action of manually operable syringes, thus generating the slight negative pressure in the syringes essential for aspiration. The syringes of the present invention therefore obviate the disadvantage inherent in prior art syringes of the manual type, since the aspirating action is generated automatically which requires no special skill on the part of the practitioner.
These and other desirable objects will be explained as the description proceeds.
The invention will be described in reference to a pre-filled syringe; however, it is to be understood that a pre-filled cartridge, having essentially the same shape and other characteristics as a pre-filled syringe, is also intended to be described and covered by the appended claims.